Running a JAR file from a java program

If you want to run a jar from a java program.

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.jar.Attributes;
import java.util.jar.JarFile;
import java.util.jar.Manifest;
 
/**
 * Call this class with the name of the jar file.
 *
 * Example:
 * java -classpath . Launcher foo.jar [arguments]
 */
public class Launcher {
 
  public static void main(String args[]) throws Exception {
    File jarfile = new File(args[0]);
    JarFile jar = new JarFile(jarfile);
    Manifest manifest = jar.getManifest();
    Attributes attrs = manifest.getMainAttributes();
    String mainClassName = attrs.getValue("Main-Class");
    URL url = new URL("file", null, jarfile.getAbsolutePath());
    ClassLoader cl = new URLClassLoader(new URL[] {url});
    Class mainClass = cl.loadClass(mainClassName);
    Method mainMethod = mainClass.getMethod("main", new Class[] {String[].class});
    String[] args2 = new String[args.length - 1];
    System.arraycopy(args, 1, args2, 0, args.length - 1);
    mainMethod.invoke(mainClass, new Object[] {args2});
  }
}